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Dynamic Clocks For Radeon R500+

04-04-2008, 07:50 PM

Phoronix: Dynamic Clocks For Radeon R500+

When it comes to ATI open-source power management, so far AMD's open-source kindness has just yielded a list of registers but no proper documentation or how PowerPlay exactly works. However, AMD's Alex Deucher has just committed "Dynamic Clocks" support for the Radeon R500 and R600 graphics cards...

However other reviews tell things still work driver dependent, so if changing power states is still a driver job, does it work with fglrx and will those specifications also become availiable for the RadeonHD team or are these processes completely transparent to the software now?

My understanding is that there is still some driver involvement, but the new HW capabilities on 6xx parts allow faster and more fine-grained power-down than the driver can do on its own so overall power savings can be improved. We will be making this information available to open source developers. In parallel, support is being added (or has been added) to fglrx although I'm not sure of the exact status.

So what I still like to know is which PowerPlay functions are implemented in hardware (and therefore should work on Linux out of the box?!), which functions are driver dependent and which will work with RadeonHD now or soon.

If you want to leak some more information, I would also like to know when RV770 will arrive

Comment

I don't think anything is completely implemented in hardware. Everything needs to be set up by the driver and AFAIK pretty much everything needs to be enabled and disabled at certain times. The difference with the newer chips seems to be that once everything is set up the hardware can make some of the clock switching decisions without driver intervention, so that power consumption can be adjusted more quickly as the workload changes and more power can be saved as a result.

Alex is experimenting with the AtomBIOS calls for dynamic clock gating but so far we aren't seeing a lot of benefit. Whenever we find something that seems useful it will probably end up in RadeonHD within a couple of days of when we find it.

Comment

Sorry to be dense, but this means there is not even a way to change it manually, i.e. at the commandline?

You can set the mode in your xserver config and it will stay as set until you change it and restart X. It's more of a proof of concept at this point. I'll be adding it to kernel modesetting where you will be able to change the settings on the fly using sysfs.

Comment

I'm actually using the latest git revision of xf86-video-radeon. The driver works beautifully. 2D performance are awesome and 3D is improving. Concerning powerplay options I'm unable to set any mode in my xorg config file. It seems that

Code:

Option "PowerPlayMode" "1,2 or 3"

is not recognized as a valid option. Am I missing something?
Thanks in advance